Features:
+* make tmpfiles read lines from creds, so that we can provision SSH host keys
+ via creds. Similar: sysusers, sysctl, homed
+
+* mount /var/ from initrd, so that we can apply sysext and stuff before the
+ initrd transition. Specifically:
+ 1. There should be a var= kernel cmdline option, matching root= and usr=
+ 2. systemd-gpt-auto-generator should auto-mount /var if it finds it on disk
+ 3. mount.x-initrd mount option in fstab should be implied for /var
+
+* implement varlink introspection
+
* we should probably drop all use of prefix_roota() and friends, and use
chase_symlinks() instead